1. Field of the Invention
The present invention relates to a light emitting display, and more particularly, to a light emitting display, in which a voltage drop in a power line is uniform, thereby providing a uniform brightness in the pixels.
2. Discussion of Related Art
Recently, various flat panel displays have been developed to replace a cathode ray tube (CRT) display, because the CRT display is relatively heavy and bulky. Flat panel display types include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panel (PDPs), light emitting display (LEDs), and similar flat panel technologies.
Light emitting displays include a plurality of light emitting devices, wherein each light emitting device emits light by electron-hole recombination or a similar process. Light emitting displays are classified into inorganic light emitting displays that include an inorganic emission layer and organic light emitting displays that include an organic emission layer. Light emitting displays have response times that are relatively fast and power consumption that is relatively low.
FIG. 1 is a plan view of a conventional light emitting display. A conventional light emitting display includes: a substrate 10, a pixel portion 20 that includes a plurality of pixels 21 formed adjacent to a region defined by a plurality of scan lines S, a plurality of data lines D and a plurality of pixel power lines VDD, which are formed on the substrate 10; a scan driver 30; a data driver 40; a first power line 50; a second pixel power line 52; and a pad hub 60.
The scan driver 30 is placed adjacent to one side of the pixel portion 20 and electrically connected to a first set of pads Ps on the pad hub 60 through a scan control signal line 32. The scan driver 30 generates scan signals in response to a scan control signal transmitted through the scan control line 32 and supplies the scan signals to the scan lines S of the pixel portion 20.
The data driver 40 is electrically connected to the data line D and the second set of pads Pd on the pad hub 60. The data driver 40 may be mounted as a chip onto the substrate 10.
The second pixel power line 52 is formed on the whole area of the pixel portion 20. The second pixel power line 52 supplies a second pixel driving voltage from the third set of pads Pvss on the pad hub 60 to each pixel 21.
The first power line 50 is placed adjacent to a top side of the pixel portion 20. The first power line 50 is commonly connected to the first ends of the first pixel power lines VDD. The first power line 50 receives the first pixel driving voltage from a first power supplying line 48 through a fourth set of pads Pvdd on the pad hub 60 and supplies it to the first pixel power line VDD of each pixel 21.
The respective first ends of the first pixel power lines VDD are commonly connected to the first power line 50. Each first pixel power line VDD supplies the first pixel driving voltage from the first power line 50 to each pixel 21.
Thus, each pixel 21 is controlled by the scan signal transmitted through the scan line S. Each pixel 21 emits light based on the current supplied from the first pixel power line VDD to the light emitting device in response to the data signal transmitted through the data line D, thereby displaying an image.
In the conventional light emitting display, the respective first pixel power lines VDD that are commonly connected to the first power line 50 are different in length, so that line resistance on the first pixel power lines is not uniform. Therefore, the voltage drop (i.e., IR drop) in the first pixel driving voltage supplied to the pixels 21 differs between pixels. That is, the voltage drop of the first pixel power line VDD becomes smaller as the first pixel power line VDD gets closer to the first power line 50, but becomes larger as it gets far away from the first power line 50. Hence, in the conventional light emitting display, the voltage drop in the first pixel power line VDD is different according to the position of the pixel 21, so that the intensity of current supplied to the pixel 21 is not uniform. Rather, the intensity of the current varies with respect to the same data signal according to the positions of the pixel 21, thereby making the brightness non-uniform.